My thought is that One Vision wasn't written for Highlander, it's in Iron Eagle. And my other thought is that Roger wanted to write song about what you've mentioned, but Freddie changed the lyrics - it doesn't mean that something based on Roger's idea was recorded.

Roger also never said it was written about Martin Luther King, he said he'd heard someone had said that Roger had written it about him (and the eye-rolling look Roger gives suggests that it obviously wasn't about MLK).